CN108411368B - Method for rapidly and selectively reducing micropipe and dislocation density in SiC crystal - Google Patents
Method for rapidly and selectively reducing micropipe and dislocation density in SiC crystal Download PDFInfo
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- CN108411368B CN108411368B CN201810592023.4A CN201810592023A CN108411368B CN 108411368 B CN108411368 B CN 108411368B CN 201810592023 A CN201810592023 A CN 201810592023A CN 108411368 B CN108411368 B CN 108411368B
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Abstract
The invention relates to a method for rapidly and selectively reducing micropipe and dislocation density in SiC crystal, which utilizes the density of the micropipe<1cm‑2Dislocation density of 5000cm or less‑2The SiC region covers the micropipe and the region with higher dislocation density, thereby blocking the extension of dislocation and the micropipe, effectively reducing the inheritance of dislocation and the micropipe, obtaining the SiC bulk single crystal with specific micropipe and dislocation density, having high selectivity, obtaining the bulk single crystal with low micropipe and dislocation by only once growth, and greatly shortening the optimization time.
Description
Technical Field
The invention relates to a method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals, belonging to the technical field of crystal growth.
Background
The SiC single crystal material is taken as a third-generation semiconductor material, has excellent electrical properties including wide forbidden band, high thermal conductivity, high electron saturation shift rate and high breakdown electric field, is considered to be an ideal semiconductor material for manufacturing optoelectronic devices, high-frequency high-power devices and power electronic devices, and has wide application in the aspects of white light illumination, optical storage, screen display, aerospace, high-temperature radiation environment, petroleum exploration, automation, radar and communication, automobile electronization and the like. The most successful and commercialized method for growing SiC crystals at present remains the Physical Vapor Transport (PVT) method.
With the gradual improvement of the quality of SiC single crystals, the diameter of SiC is larger and the defect density is lower. For SiC growers, the density of micropipes is effectively controlled. However, the SiC material itself still has a relatively high dislocation density, which is generally 103-105cm-2The presence of dislocations degrades device performance and affects long term reliability for the device.
More and more research is focused on the mechanism of defect formation and attempts are being made to reduce defect density. Daisuke Nakamura et al, teaches that repeating the a-plane yields SiC single crystals free of micropipes and ultra-low dislocations. But this method is achieved through multiple growths. Li et al suggest that crystals with zero micropipes can be obtained by growth with (01-14) planes, but that the obtained crystal diameters are small and cannot be compared with commercial 2-6inch single crystals. Sakwe alloysius Sakwe et al discuss the effect of different doping with type N, P on dislocation density. Although the dislocation density distribution can be changed by doping, the dislocation density cannot be reduced.
It can be seen that there is no effective way to improve the quality of SiC single crystals and reduce micropipe and dislocation density at this stage. Therefore, it is desirable to provide a crystal method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for rapidly and selectively reducing the micropipe and dislocation density in the SiC crystal.
The technical scheme of the invention is as follows:
a method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals, comprising the steps of:
(1) selecting microtube Density<1cm-2Dislocation density of 5000cm or less-2And cutting the SiC region into a symmetrical crystal with a polar surface on the side surface;
(2) fixing the symmetrical crystal cut in the step (1) in a multi-micropipe multi-dislocation area of the SiC seed crystal;
(3) carrying out two-stage crystal growth on the SiC seed crystal treated in the step (2), wherein in the first stage: low temperature and low pressure to promote lateral growth and form full sheet micro tube density<5cm-2Density of dislocations<5000cm-2The second stage: and growing under the condition of approximate equilibrium state.
Preferably, according to the invention, the crystal form of the crystal in the step (1) is consistent with the crystal form of the SiC seed crystal in the step (2).
According to a preferred embodiment of the invention, the micropipe density of the crystals in step (1)<0.1cm-2Dislocation density of 10 or less3cm-2。
According to the invention, the crystal cut in the step (1) is a crystal with 3-time and 6-time symmetry, the side surface of the crystal is a polar surface, and the polar surface is (1-100) and/or (11-20).
According to the present invention, it is preferable that the crystal cut in step (1) is subjected to high-temperature annealing or polishing to remove the cut damage layer.
Preferably, in step (2), the SiC seed crystal is a seed crystal larger than 4 inches, and the crystal form is 4H, 6H, 3C or 15R.
Further preferably, the SiC seed is a 4 inch seed, a 6inch seed, an 8 inch seed, or a 16 inch seed.
According to the invention, in the step (2), the fixing mode is preferably a graphite glue or metal plating mode.
Preferably, in step (3), the low-temperature and low-pressure growth is as follows: the growth time is 2-20h under the conditions that the temperature is 200 ℃ lower than the growth temperature and the pressure is 0.1-30 mbar.
Further preferably, the low-temperature low-pressure growth temperature is 1700-.
Preferably, in step (3), the lateral growth rate is greater than 8um/h and the axial growth rate during the seed treatment stage is less than 60 um/h.
Further preferably, in the step (3), the lateral growth rate is 10-20um/h, and the axial growth rate in the seed crystal treatment stage is 40-50 um/h.
Preferably, in the step (3), the growth conditions approximate to the equilibrium state are that the temperature difference between the source material and the seed crystal is less than 100 ℃; the pressure is 5-15 mbar.
Further preferably, the growth condition of the approximate equilibrium state is that the temperature difference between the source material and the seed crystal is 60-80 ℃; the pressure is 8-12 mbar.
Preferably, according to the present invention, the growth method of step (3) is PVT, HTCVD or liquid phase growth method.
The principle of the invention is as follows:
dislocations and micropipes are typical structural defects in SiC single crystals, and micropipes are considered to be dislocations with large Burgers vectors based on Frank theory. In SiC growth, dislocations and micropipes are along [0001 ]]The direction is extended. The present invention takes advantage of the density of micropipes, which may extend from the seed into the crystal during growth along the (001) plane, resulting in the genetic transmission of micropipes and dislocations from the seed to the bulk crystal<1cm-2Dislocation density of 5000cm or less-2The SiC area covers the micropipe and the area with higher dislocation density, thereby blocking the extension of the dislocation and the micropipe and effectively reducing the inheritance of the dislocation and the micropipe. The invention can selectively optimize the quality of the single crystal, and can obtain the bulk crystal with low micropipe and low dislocation by only one-time growth.
The invention has the beneficial effects that:
1. the invention utilizes the density of the microtubes<1cm-2Dislocation density of 5000cm or less-2The SiC area covers the micropipe and the area with higher dislocation density, thereby blocking the extension of the dislocation and the micropipe, effectively reducing the inheritance of the dislocation and the micropipe, obtaining the SiC bulk single crystal with specific micropipe and dislocation density and having high selectivity.
2. The method can obtain the bulk single crystal with low micropipe and dislocation only by once growth, thereby greatly shortening the optimization time.
3. The method is particularly beneficial to improving the local quality of the SiC substrate with the diameter of more than 100mm and improving the growth efficiency of the large-diameter substrate.
Drawings
FIG. 1 is a schematic view showing the structure of a growth chamber for growing SiC crystals by a Physical Vapor Transport (PVT) method in Experimental example 1;
1. a graphite fiber heat-insulating layer, 2, a gap between the upper heat-insulating material and the top of the crucible, 3, seed crystals, 4, the crucible, 5, a gap between the side heat-insulating material and the side wall of the crucible, and 6, source material powder.
FIG. 2 is a schematic view of a multi-micropipe distribution structure of a SiC substrate before being optimized;
FIG. 3 is a graph showing the use of micropipe density<1cm-2Dislocation density of 5000cm or less-2The SiC area covers the structure schematic diagram of the upper area of the micropipe;
figure 4 is a schematic view of the micropipe distribution structure of the 150mm SiC seed crystal after being optimized.
Detailed Description
The present invention will be further illustrated by the following examples, but the present invention is not limited to the following examples.
Example 1:
a method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals, comprising the steps of:
(1) selecting microtube Density<0.1cm-2Dislocation density of 10 or less3cm-2Cutting the SiC area of the crystal into 6-time symmetric crystals with polar surfaces on the side surfaces, and polishing the cut crystals to remove a cut damage layer;
(2) fixing the symmetrical crystal processed in the step (1) in a multi-micropipe multi-dislocation area of the SiC seed crystal by adopting graphite glue, wherein the crystal form of the crystal in the step (1) is consistent with that of the SiC seed crystal in the step (2);
(3) carrying out two-stage crystal growth on the SiC seed crystal treated in the step (2), wherein in the first stage: promoting lateral growth at low temperature and low pressure, wherein the growth temperature at low temperature and low pressure is 1700 ℃, the pressure is 1mbar, and the growth time is 10 hours; forming a full sheet of microtubes<5cm-2Density of dislocations<5000cm-2The lateral growth rate of the complete seed crystal is 15um/h, and the axial growth rate of the seed crystal in the seed crystal treatment stage is 50 um/h; and a second stage: growing under the condition of approximate equilibrium state growth; the approximate equilibrium growth condition is that the temperature difference between the source material and the seed crystal is 80 ℃; the pressure is 12 mbar.
Specific experimental examples:
aiming at the problems that the existing large-size SiC crystal has long development period for optimizing and improving quality and is difficult to reduce the density of micropipes and dislocation, the experimental example is a method for growing SiC single crystal based on a physical vapor transport technology, and the method of the embodiment 1 is adopted to obtain the high-quality SiC crystal bar.
The structure of a growth chamber for growing SiC crystals by a Physical Vapor Transport (PVT) method in an experimental example is shown in figure 1, a crucible is arranged in a growth cavity, source material powder is filled at the bottom of the crucible, seed crystals are fixed on a crucible cover, and a graphite fiber heat-insulating layer is arranged outside the growth cavity.
The seed crystal 9 is a 6inch, 4HSiC substrate material; the microtube distribution obtained by the microtube test method is shown in fig. 2. There are two areas of microtubule aggregation, concentrated at 20 × 30cm2And 40 x 40cm 2.
Selecting 3inch4H-SiC monocrystal substrate material with micropipe density less than 0.5cm-2Dislocation density of 2000cm-2. 6-degree symmetric crystals with polar faces on the sides, namely 7 and 8 in figure 3, are cut, and the edges of the crystals are (1-100) faces. Regions 7 and 8 are annealed at 1500 deg.c and polished to remove the damaged layer. And fixing the area needing to be optimized of the 150mm seed crystal 9 by using carbon glue.
Growing the crystal by physical vapor transmission technology, performing the first step of growth, and promoting the lateral growth by adopting the growth temperature of 1850 ℃ and the pressure of 4mbar and adopting the mixed gas of argon and nitrogen as carrier gas to form complete seed crystals. Then, the temperature is raised to the growth temperature of 2200 ℃, and SiC single crystal growth is carried out by adopting 100 mbar. Cutting and measuring the optimized distribution of the microtubes after the growth is finished; the distribution structure of the micropipes of the optimized 150mm SiC seed crystal is shown in figure 4, so that the micropipes are effectively reduced, the bulk single crystal with low micropipes can be obtained by one-time growth, the optimization time is greatly shortened, the local quality of the SiC substrate with the diameter of 150mm is improved, and the growth efficiency of the large-diameter substrate is improved.
Example 2:
a method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals, comprising the steps of:
(1) selectingDensity of micropipe<0.1cm-2Dislocation density of 10 or less3cm-2Cutting the SiC area of the crystal into 3-time symmetric crystals with polar surfaces on the side surfaces, and polishing the cut crystals to remove a cut damage layer;
(2) fixing the symmetrical crystal processed in the step (1) in a multi-micropipe multi-dislocation area of the SiC seed crystal by adopting graphite glue, wherein the crystal form of the crystal in the step (1) is consistent with that of the SiC seed crystal in the step (2);
(3) carrying out two-stage crystal growth on the SiC seed crystal treated in the step (2), wherein in the first stage: promoting lateral growth at low temperature and low pressure, wherein the growth temperature at low temperature and low pressure is 1900 ℃, the pressure is 2mbar, and the growth time is 8 hours; forming a full sheet of microtubes<5cm-2Density of dislocations<5000cm-2The lateral growth rate of the complete seed crystal is 20um/h, and the axial growth rate of the seed crystal in the seed crystal treatment stage is 40 um/h; and a second stage: growing under the condition of approximate equilibrium state growth; the approximate equilibrium growth condition is that the temperature difference between the source material and the seed crystal is 60 ℃; the pressure is 12 mbar.
Claims (9)
1. A method for rapidly and selectively reducing micropipe and dislocation density in SiC crystals, comprising the steps of:
(1) selecting microtube Density<1cm-2Dislocation density less than 5000cm-2And cutting the SiC region into a symmetrical crystal with a polar surface on the side surface;
(2) fixing the symmetrical crystal cut in the step (1) in a multi-micropipe multi-dislocation area of the SiC seed crystal;
(3) carrying out two-stage crystal growth on the SiC seed crystal treated in the step (2), wherein in the first stage: low temperature and low pressure promote lateral growth to form full sheet micro tube density<5cm-2Density of dislocations<5000cm-2The second stage: growing under the condition of approximate equilibrium state growth; the approximate equilibrium growth condition is that the temperature difference between the source material and the seed crystal is 60-80 ℃; the pressure is 8-12 mbar.
2. Rapid selective reduction of microminiature in SiC crystals according to claim 1The method for controlling the tube and dislocation density is characterized in that the crystal form of the crystal in the step (1) is consistent with that of the SiC seed crystal in the step (2); micropipe density of crystal<0.1cm-2Dislocation density of 10 or less3cm-2。
3. The method for rapidly and selectively reducing the micropipe and dislocation density in the SiC crystal according to claim 1, wherein the crystal cut in the step (1) is a crystal with 3-order and 6-order symmetry, the side surface of the crystal is a polar surface, and the polar surface is a (1-100) or (11-20) surface; and removing the cut damage layer of the cut crystal through high-temperature annealing or polishing.
4. The method for rapidly and selectively reducing micropipe and dislocation density in a SiC crystal according to claim 1, wherein in step (2), the SiC seed crystal is a seed crystal of greater than 4 inches and has a crystal form of 4H, 6H, 3C or 15R.
5. The method for rapidly and selectively reducing the micropipe and dislocation density in the SiC crystal according to claim 1, wherein in the step (2), the fixing mode is a graphite glue or metal coating mode.
6. The method for rapidly and selectively reducing the micropipe and dislocation density in an SiC crystal according to claim 1, wherein in step (3), the low temperature and low pressure growth is: the growth time is 2-20h under the conditions that the temperature is 200 ℃ lower than the growth temperature and the pressure is 0.1-30 mbar.
7. The method for rapidly and selectively reducing the micropipe and dislocation density in SiC crystals as claimed in claim 6, wherein the low temperature and low pressure growth temperature is 1700-2200 ℃, the pressure is 0.5-5mbar, and the growth time is 8-10 h.
8. The method for rapidly and selectively reducing micropipe and dislocation density in an SiC crystal according to claim 1, wherein in step (3), the lateral growth rate is greater than 8um/h and the axial growth rate during the seed treatment stage is less than 60 um/h.
9. The method for rapidly and selectively reducing the micropipe and dislocation density in an SiC crystal according to claim 8, wherein in step (3), the lateral growth rate is 10-20um/h and the axial growth rate in the seed crystal treatment stage is 40-50 um/h.
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